As much as I hate the thought of trying to do physics in imperial units, I can understand the benefit for some people.
It shouldn't be that hard to adopt weights to fit varying planets, as long as the unit of gravity of the planet is a ratio to the baseline used for the items weight. For example if the book assumes earth like gravity (G0=~9.81 m/s^2) for the equipment, a planet (G1) with two times the mass should have approximately twice the attractive force (G1=~2xG0) so long as the planet is much larger than your equipment. So just double all the weights (weight is force, and if the gravitational acceleration doubles and the items mass stays the same, the force doubles as well). If the planet has 3.6x the gravity of earth multiply the items weight by 3.6x. It's that simple.
While the size of a planet and it's mass aren't directly related I can't see too many instances where you'd land on a superdense rock the size of a neighborhood block, and if you are then gravity wouldn't behave quite the way we're used to here on earth anyways. If there were rules for calculating gravity and it's effects on any possible astral body he'd need to make the rulebook thicker than a university textbook.